There have recently been developed and utilized in various industrial fields some composite materials comprising an inorganic fiber (e.g. alumina fiber, silica fiber, silicon carbide fiber, boron fiber, etc.) and a matrix consisting of a metal selected from aluminum, magnesium, copper, nickel, titanium, etc. or an alloy thereof.
When the metals or metal alloys as mentioned above are reinforced with the inorganic fiber, a reaction proceeds at the interface of the inorganic fiber and the molten or high temperature metals or metal alloys to form a brittle layer, which causes a lowering of the strength of the composite material, and thereby, the composite material exhibits lower strength than the theoretical one. For instance, a commercially available carbon fiber has a strength of about 300 kg/mm.sup.2, and it is used for reinforcing metals or metal alloys, assuming that the fiber material will occupy 50% by volume in the composite material, the composite material will theoretically have a strength of about 150 kg/mm.sup.2 even though the strength due to the matrix material is neglected. In fact, in the case of a carbon fiber-reinforced composite material using a matrix of an epoxy resin, the composite material has a strength of about 150 kg/mm.sup.2 or more. However, when a matrix of aluminum is used and the composite material is prepared therewith by a molten metal impregnating method, the resulting carbon fiber-reinforced composite material has a strength of about 30-40 kg/mm.sup.2. This is due to the interfacial reaction induced by contacting the fiber with a molten metal and thereby deteriorating the properties of the carbon fiber. It has been proposed to improve such deterioration of fibers by various means, for example, by treating the surface of the fiber with a coating agent, but this method is not practically suitable because of troublesome handling and/or the high cost.